Observation state of the campaign

[Ernst Pollmann]

Dear colleagues,
I would like to introduce the current state of our Halpha monitoring.

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Comments are welcome!
Ernst

[Ernst Pollmann]

Dear colleagues,
I would like to inform you about the current state of the campaign:

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The Hα components V&R in the emission strength (EW) (Fig. 2) and peak height (Fig. 3) show as expected the currently intensity decrease in analogy to the Vmag decrease (Fig. 1).
The eclipse of VV Cep has never been observed as dense as this time. Even if the variability of the fine structure of the Hα components shows an enigmatic behavior, this is the first time that this becomes apparent in this form.
How we have to understand this behavior in conjunction with the periodic precession of the disk rotation axis, as manifested in the V/R plot (Figure 4) is still unclear. It will be interesting to see how this dynamic looks, the closer the total eclipse comes.

Ernst Pollmann

[Ernst Pollmann]

Dear colleagues,
here a sumary of the Halpha V/R periodic behavior.
Fig. above: V/R time series with a long-term period
Fig. middle: Scargle periodogram (power spectrum) of time series data subtracted by long-term period. Period = 41.5 days
Fig. bottom: Phase diagram of the 41.5 d period.
Interpretation: confirmation of nodding (precession) of the accretion disk? More data are required.

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Ernst Pollmann

[Ernst Pollmann]

Dear colleagues,
I would like inform about the current state of the Halpha campaign results:

Total monitoring of the Halpha EW:

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V/R periodicity as indicator of precession of the disk rotational axis:

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Comments are welcome!
Ernst Pollmann

[marcoastro+]

Dear Ernst,


The more observations are appearing, the more our initial "hunch" of a possible wobble/precession behaviour can explain the course of the corrected V/R diagram.
The Scargle periodogram shows a significant cycle of approx. 41-42 days.
The small changes between the consecutive periods could be caused by accretion disc dynamics, as a result of unequal mass distribution.
Thermonuclear mini-bursts are probably absent as the light curve analysis doesn't indicate such a behaviour.
I think this is the first time report of such a detailed observation of this proposed behaviour within the VV Cephei binary complex.
Together with further professional teamwork results it deserves an interesting article for journals as A&A or AJ.
Perhaps attempts for synthetic spectra calculated by PHOEBE modelling would be also interesting to compare with our results.

Many thanks to all members/colleagues for their ongoing efforts, despite sometimes disappointing weather conditions.
To fully understand what happens more observations are needed.


Kind regards,
Marc.

[Ernst Pollmann]

Dear Marc,
let me offer some thoughts to the observed phenomenon:
it seems highly unlikely that the pulsation process of the M star would produce regular density variations in the outer atmosphere of the star, which could explain the 42 d V/R period of the partially eclipsed disk. However, nodding oscillations of the disk, caused by the precession of the rotational axis, as encountered in decretion disks of Be stars (Martin et al., 2011; Schaefer et al., 2010), could plausibly explain the periodic V/R variation. The causes of precessions are not clear, but Hummel (1998) suggested that they might be induced by tides from a binary companion.

The clearly detected period of "only" about 42 days might mean that the mass and/or the diameter of the accretion disk must also be "correspondingly small".

Recently, a 440-day precession period of the decretion disk rotation axis was detected in the Be binary system ζ Tau (Pollmann, 2017, IBVS No. 6208). This occurred during a time period when the disk mass was in its minimum. During the same time period this disk mass of ζ Tau was defined by Tycner & Sigut (2015) as ~ 1.2*10^-10 mass of the primary star. Since the mass of the primary = 11.3 solar masses (SM) (Carciofi et al. 2009), the mass of the disk in ζ Tau was 11.3 SM * 1.2 *10^-10 = 1.356*10^-9 SM.

In general, the precession of Be star disks is proportional to their mass and diameter (Martin et al. 2011). The precession period of the accretion disk in VV Cep, with 42 d, is a tenth of the precession period of the disk in ζ Tau (440 d).

Since the mass of the B star in VV Cep (18.6 SM; Bennett et al. 2004) is approximately of the same order of magnitude of the Be star ζ Tau, can we say that the mass of the VV Cep accretion disk is also a tenth of the disk mass in ζ Tau = 1.356 *10^-10 SM?

Best wishes,
Ernst

[Ernst Pollmann]

Dear colleagues,
Here I would like to introduce the current, self-explained "high resolution spectroscopical " observation state of the VV Cep campaign:

1) Strongly time synchronic behavior of the Halpha V and R component > indicator for a "relatively" small disk?

2) The short-term variability (42 d precession period of the disk rotational axis) is going on further (V/R plot)

3) The 2. contact T2, calculated from the last eclipse as 2017-10-27, will be take place assumable at the beginning of december (or so). This time difference could be an additionally indicator for a smaller disk then during the last eclipse 1997/99.

Comments 1-3 had been discussed / presented on the "Spectroscopy Day" yesterday at the "TIVOLI" observatory Oudenbosch, Netherland.

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Ernst Pollmann

[HughAllen]

This is very interesting data Ernst. The cyclic variability in the intensity of the Hα emission is beautifully on display. Despite the low frequency of observation I think we luckily caught the cycle peaks in mid-September and late October in our low resolution Alpy data. Have I understood correctly, that the cycles may be due to changes in the angle of the gas disc to our line of sight?
Cheers
Hugh

[Ernst Pollmann]

... yes Hugh, you understood that right.
It seems highly unlikely that the pulsation process of the M star would produce regular density variations in the outer atmosphere of the star, which could explain the 42 d V/R period of the partially eclipsed disk.
However, nodding oscillations of the disk, caused by the precession of the rotational axis, as encountered in decretion disks of Be stars (Martin et al., 2011; Schaefer et al., 2010), could plausibly explain the periodic V/R variation.
The causes of precessions are not clear, but Hummel (1998) suggested that they might be induced by tides from a binary companion.
The clearly detected period of "only" about 42 days might mean that the mass and/or the diameter of the accretion disk must also be "correspondingly small".
For a better understanding, the following link shows an animation of the disk nodding of zeta Tau, based on investigation of Schaefer et al. in "The Astronomical Journal" 140, 1838-1849, 2010:
http://astrospectroscopy.de/media/files ... g_slow.AVI

Best wishes,
Ernst

[Ernst Pollmann]

Dear colleagues,
in addition to the campaign state above, here the period analysis of the V/R oscillation. The fantastic high observation density enables to determine the periodic behavior more precisely. It is now 43.7 (+/-) 0.32 d.
It is great that some colleagues of the group have such high energy and obviously excellent observation conditions in order to contribute to this unique result.
I would like to thank you very much.

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Ernst Pollmann